[mythtv-users] 1920x1080 vs. 1920x1088 HDTV streams

Doug Larrick doug at ties.org
Fri May 20 00:07:49 UTC 2005

Bernd Paysan wrote:
> The main difference is obvious when switching from ProSieben to HD1:
> 2005-05-19 22:41:44.184 AvFormatDecoder: Video has changed from 
> 1920x1080 to 1920x1088.
> Apparently the 1920x1088 mode is decoded fine, while the 1920x1080 
> doesn't. 

Interesting that you have a video that's 1080 lines high.  Here in the
US all the "1080i" content that we have is actually 1088 lines, with the
bottom 8 lines defined to be blank.  MythTV actually has special code
that sets the output to 1080 lines if it is given a 1088-line video, to
avoid a black band at the bottom, and avoid scaling when outputting to a
1080-line display.

The macroblocks in the ATSC MPEG stream are 16 pixels high, which is an
integer divisor of 1088 but not 1080.  A 1080-line video would imply
that the macroblocks are 8 (or 4; unlikely) pixels high.  I can see this
breaking a decoder or being beyond the capability of some system.

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